Propagation delay

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Propagation delay is a term for in electroacoustics and sound engineering

  1. the delay in the sound radiation from loudspeakers compared to a primary sound source in the context of sound reinforcement technology using the Haas effect
  2. the delay of sound signals for the purpose of time correction
  3. the delay for the purpose of artistic creation (manipulation) of a sound recording

With decentralized sound reinforcement , i.e. when broadcasting for a large audience in stereophony and in surround sound technology, double or multiple listening and, as a result, reduced syllable intelligibility or reduced transparency (acoustics) can occur if the transit time difference between the sound events of the distributed loudspeakers and possibly the original sound at the listener's ear exceeds 50 ms, corresponding to a path difference of about 17 m, or if the sound level differences Δ L are greater than 6 dB; see also echo threshold . If both apply, the different sound transit times must be adjusted to avoid the deficiencies described. In order to continue to guarantee the localization of the original sound source (primary sound source), it must also be ensured that the original sound (primary sound) arrives at the listener a few milliseconds earlier than the delayed loudspeaker sound, whereby this is up to 10 dB above the level of the Original sound can be located without impairing the localization process; see also the Haas effect .

For the time delay of signals, purely electronic delay devices, predominantly in digital technology , have established themselves . If, for example, an original sound event is to be emitted by loudspeakers that are arranged at different distances from the sound source (the sound body), one thinks of concentric circles around the original sound source and delays the sound radiation of all loudspeakers lying on such a circular line by the duration of the sound corresponding to the radius . The listeners are then exposed to sound in-phase from all loudspeakers in front of them in the direction of the original sound source, while the loudspeakers located backwards and to the side are practically imperceptible due to their directional characteristics .

In the case of sound recordings with several microphones at different distances from the sound source, the microphone signals can be brought “in phase” by delaying the propagation time, so that frequency-dependent partial cancellations when mixing or at the listening position are avoided. This is the technique of delayed support microphones , which is sometimes used for sound recording .

With transit time delays, the impression of additional room depth can be created. Furthermore, transit time delays serve to artificially simulate early sound reflections or reverberation and also contribute to the spatial impression .

See also

literature

  • Siegfried Wirsum: Practical sound reinforcement technology. Device concepts, installation, optimization. Franzis-Verlag GmbH, Munich 1991, ISBN 3-7723-5862-4 .
  • Rolf Beckmann: Manual of PA technology. Basics, components, practice. 2nd Edition. Elektor-Verlag, Aachen 1990, ISBN 3-921608-66-X .

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